A laser delay measurement device and method based on fundamental light modulation sampling

Abstract

This invention provides a laser delay measurement device and method based on fundamental frequency optical modulation sampling, addressing the technical problems of existing methods using balanced optical cross-correlation (BOC) for delay measurement and synchronization. These problems include the inability of a single BOC to simultaneously achieve high precision and a wide range, and the decrease in measurement accuracy as the laser pulse width increases, leading to complex pulse synchronization systems. The measurement device of this invention includes a first aperture. One laser beam passing through a large aperture on the first aperture is used as the pump light, while another laser beam passing through two small apertures on the first aperture serves as the first and second signal lights. A first birefringent crystal and a second birefringent crystal are used to introduce a delay difference between the first and second signal lights. By moving the delay line on the first or second reflector and sampling the light intensities of the first and second signal lights under different delays, the fundamental frequency modulation intensity difference between the first and second signal lights can be obtained.

Description

Technical Field

[0001] This invention relates to ultrashort laser pulses, and more particularly to a laser delay measurement device and method based on fundamental frequency optical modulation sampling. Background Technology

[0002] With the development of ultra-intense and ultra-short laser technology, higher demands are being placed on laser output power, providing more extreme research methods for disciplines such as strong-field physics, condensed matter physics, chemistry, and biomedicine. Laser coherent beam combining technology is one of the effective ways to achieve higher power output. Measuring and calibrating the delay of multiple laser pulses is a very important and challenging research task.

[0003] For ultrashort pulse lasers, the balanced optical cross-correlation method is commonly used for delay measurement and synchronization, and this method has been well-validated internationally. However, due to limitations in the measurement principle, a single balanced optical cross-correlation unit (BOC) cannot simultaneously achieve high measurement accuracy and a wide measurement range. Furthermore, the measurement accuracy decreases as the laser pulse width increases, making the pulse synchronization system complex. Summary of the Invention

[0004] The purpose of this invention is to solve the technical problems of existing methods for delay measurement and synchronization using balanced optical cross-correlation, where a single BOC cannot achieve both high measurement accuracy and a wide measurement range, and the measurement accuracy decreases as the laser pulse width increases, leading to a complex pulse synchronization system. The invention provides a laser delay measurement device and method based on fundamental frequency optical modulation sampling.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A laser delay measurement device based on fundamental frequency light modulation sampling is characterized in that it includes a first aperture, a first birefringent crystal, a second birefringent crystal, a first mirror, a second mirror, a concave mirror, a medium, an obstruction, a second aperture, a third aperture, a first lens, a second lens, and a balanced photoelectric probe.

[0007] The first aperture is located in the incident light path of the two ultrashort pulse lasers to be tested. The first aperture has a large aperture and two small apertures of the same size. One incident laser beam passes through the large aperture and is used as pump light. The other incident laser beam is split into two beams through the two small apertures and used as the first signal light and the second signal light. The area of ​​the large aperture needs to ensure that the energy of the transmitted pump light is greater than 7 μJ. The area ratio of the small aperture to the large aperture is 1:25 to 1:36.

[0008] The first or second reflector is provided with a delay line to change the relative delay between the first signal light, the second signal light and the pump light; the first and second reflectors are located on the same plane when the relative delay between the first signal light, the second signal light and the pump light is 0.

[0009] The focal length of the concave mirror is chosen to ensure that the pump light focusing intensity is greater than 5 × 10⁻⁶. 12 W / cm 2 ;

[0010] The second reflector, the concave mirror, the medium, and the blocking object are located sequentially on the incident light path of the pump light; after the pump light is reflected sequentially by the second reflector, the concave mirror, and the medium, it is completely blocked by the blocking object.

[0011] The first and second birefringent crystals have the same thickness and their optical axes are perpendicular to each other, which is used to introduce a delay difference between the first signal light and the second signal light; the second and third apertures are both provided with a shield in the central region and the edge region is used for transmission.

[0012] The first birefringent crystal, the first reflecting mirror, the concave mirror, the medium, the second aperture, the first lens, and the balanced photodetector are sequentially located on the incident light path of the first signal light; after being transmitted through the first birefringent crystal, the first signal light is reflected sequentially by the first reflecting mirror, the concave mirror, and the medium, and then focused onto the balanced photodetector through the edge region of the second aperture and the first lens;

[0013] The second birefringent crystal, the first reflecting mirror, the concave mirror, the medium, the third aperture, the second lens, and the balanced photodetector are located sequentially on the incident light path of the second signal light. After being transmitted through the second birefringent crystal, the second signal light is reflected sequentially by the first reflecting mirror, the concave mirror, and the medium, and then focused onto the balanced photodetector through the edge region of the third aperture and the second lens.

[0014] Furthermore, a gap of 1mm-2mm is maintained between the first and second reflectors;

[0015] The distance between the two small holes and the large hole is greater than or equal to 2mm.

[0016] Furthermore, the straight-line distance between the two smaller holes on opposite sides is equal to the diameter of the larger hole.

[0017] Furthermore, the first and second reflectors are D-shaped mirrors, which are symmetrically arranged on both sides of the gap, with the side closest to the gap being a straight edge.

[0018] Furthermore, the gap between the first reflector and the second reflector is 1 mm;

[0019] The distance between the two small holes and the large hole is 2mm;

[0020] The spacing between the pinholes is 3mm.

[0021] Furthermore, the medium is fused silica or SiO2.

[0022] Furthermore, both the second and third apertures are thin glass sheets that block the central area and transmit light at the edge area.

[0023] Furthermore, the delay line is formed by placing the first reflector on a movable platform and moving the movable platform back and forth in a direction perpendicular to the first reflector. Preferably, the movable platform is a piezoelectric ceramic displacement stage.

[0024] Furthermore, the delay line is formed by placing the second reflector on a movable platform and moving the movable platform back and forth in a direction perpendicular to the second reflector. Preferably, the movable platform is a piezoelectric ceramic displacement stage.

[0025] Based on the aforementioned laser delay measurement device based on fundamental frequency optical modulation sampling, this invention also provides a laser delay measurement method based on fundamental frequency optical modulation sampling, characterized by the following steps:

[0026] 1】Moving delay line, using pump light at different delays to perturb the light fields of the first signal light and the second signal light on the surface of the medium to form fundamental frequency light modulation, and sampling the light intensity of the first signal light and the light intensity of the second signal light at different delays through a balanced photodetector to obtain the fundamental frequency light modulation intensity curve of the first signal light and the fundamental frequency light modulation intensity curve of the second signal light at different delays, and then outputting the fundamental frequency light modulation intensity difference between the first signal light and the second signal light;

[0027] 2. Determine whether the fundamental frequency modulation intensity difference between the first signal light and the second signal light output by the balanced photodetector is 0. If it is, there is no delay between the two ultrashort pulse lasers under test. If not, there is a delay between the two ultrashort pulse lasers under test. The delay error between the two ultrashort pulse lasers under test is obtained based on the fundamental frequency modulation intensity difference between the first signal light and the second signal light.

[0028] The advantages of this invention compared to the prior art are as follows:

[0029] 1. The present invention provides a laser delay measurement device based on fundamental frequency light modulation sampling. A delay line is set on a first or second reflector to change the relative delay between the first signal light, the second signal light and the pump light. By using the pump light to perturb the light field of the first and second signal lights on the surface of the medium under different delays, the fundamental frequency light intensity is modulated, and the linear relationship between the laser delay and the fundamental frequency light modulation intensity is obtained, so as to realize the measurement and synchronization of the delay between laser pulses. The measurement device of the present invention is based on all optical devices and total reflection optical path, and the system is simple to operate and has high measurement accuracy.

[0030] 2. The laser delay measurement device based on fundamental frequency light modulation sampling provided by the present invention maintains a gap of 1mm-2mm between the first reflector and the second reflector, which can avoid the influence of moving the delay line on the first reflector and thus ensure the measurement accuracy.

[0031] 3. The present invention provides a laser delay measurement device based on fundamental frequency light modulation sampling. Both the first and second reflectors are set as D-shaped mirrors, which reduces the footprint of the first and second reflectors while increasing the size of the light spot formed.

[0032] 4. The present invention provides a laser delay measurement method based on fundamental frequency light modulation sampling. By changing the relative delay between the first signal light, the second signal light and the pump light, the light intensity of the first signal light and the second signal light under different delays are sampled respectively to obtain the fundamental frequency light modulation intensity difference between the first signal light and the second signal light. Then, the fundamental frequency light modulation intensity difference between the first signal light and the second signal light is used to determine whether there is a delay between the two ultrashort pulse lasers to be measured and to obtain the delay error. The measurement method is simple, fast and has high measurement accuracy. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of an embodiment of a laser delay measurement device based on fundamental frequency optical modulation sampling according to the present invention;

[0034] Figure 2 This is a schematic diagram of the fundamental frequency modulation intensity curves of the first signal light and the second signal light under different delays, obtained in step 1 of the measurement method embodiment of the present invention.

[0035] Figure 3 This is a schematic diagram showing the linear relationship between the fundamental frequency modulation intensity difference curve of the first signal light and the second signal light and the laser delay in step 2 of the measurement method embodiment of the present invention.

[0036] The specific reference numerals in the attached figures are as follows:

[0037] 1-First aperture; 2-First birefringent crystal; 3-Second birefringent crystal; 4-First reflecting mirror; 5-Second reflecting mirror; 6-Concave mirror; 7-Medium; 8-Obstruction; 9-Second aperture; 10-Third aperture; 11-First lens; 12-Second lens; 13-Balanced photodetector; 14-Delay line. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0039] A laser delay measurement device based on fundamental frequency optical modulation sampling, such as Figure 1 As shown, it includes a first aperture 1, a first birefringent crystal 2, a second birefringent crystal 3, a first reflector 4, a second reflector 5, a concave mirror 6, a medium 7, an obstruction 8, a second aperture 9, a third aperture 10, a first lens 11, a second lens 12, and a balanced photodetector 13.

[0040] In this embodiment, the two ultrashort pulse lasers under test are provided by a Ti:sapphire femtosecond laser with a center wavelength of 800 nm and a pulse width of 30 fs. A first aperture 1 is located in the incident light path of the two ultrashort pulse lasers under test. The first aperture 1 has a large aperture and two small apertures of the same size. One ultrashort pulse laser beam passes through the large aperture and serves as the pump light, while the other ultrashort pulse laser beam is split into two beams through the two small apertures, serving as the first signal light and the second signal light. The area of ​​the large aperture needs to ensure that the transmitted pump light energy is greater than 7 μJ. The area ratio of the small aperture to the large aperture can be selected between 1:25 and 1:36; in this embodiment, the area ratio is 1:36. The straight-line distance between the two small apertures on opposite sides is equal to the diameter of the large aperture; in this embodiment, it is 3 mm. The spacing between the two small apertures and the large aperture needs to ensure that the two laser beams under test do not interfere with each other; empirically, the spacing usually needs to be greater than or equal to 2 mm, preferably 2 mm.

[0041] The second reflector 5, concave mirror 6, medium 7, and obstruction 8 are sequentially located on the incident light path of the pump light. In this embodiment, a delay line 14 is provided on the second reflector 5 to change the relative delay between the first signal light, the second signal light, and the pump light. Simultaneously, the first reflector 4 and the second reflector 5 are located on the same plane when the relative delay between the first signal light, the second signal light, and the pump light is 0. In other embodiments of the invention, a delay line can also be provided on the first reflector 4 to change the relative delay between the first signal light, the second signal light, and the pump light. Preferably, in this embodiment, the delay line 14 is formed by placing the second reflector 5 on a movable platform and moving the movable platform back and forth in a direction perpendicular to the second reflector 5. Specifically, the movable platform is a piezoelectric ceramic displacement stage. The invention forms the delay line 14 by moving the piezoelectric ceramic displacement stage back and forth to change the relative delay between the first signal light, the second signal light, and the pump light. In other embodiments of the invention, other forms of delay lines 14 can also be used. Meanwhile, in this embodiment, the focal length of the concave mirror 6 is 200mm, which ensures that the pump light focusing intensity is greater than 5×10. 12 W / cm 2 The medium 7 can be a dielectric material such as fused silica or SiO2. In this embodiment, fused silica with a thickness of 100μm is selected. The pump light is reflected sequentially by the second reflecting mirror 5 and the concave mirror 6, and then focused onto the surface of the medium 7 by the concave mirror 6. After being reflected by the medium 7, it is completely blocked by the object 8.

[0042] The first birefringent crystal 2, the first reflecting mirror 4, the concave mirror 6, the medium 7, the second aperture 9, the first lens 11, and the balanced photodetector 13 are sequentially located on the incident light path of the first signal light. The second birefringent crystal 3, the first reflecting mirror 4, the concave mirror 6, the medium 7, the third aperture 10, the second lens 12, and the balanced photodetector 13 are sequentially located on the incident light path of the second signal light. The first birefringent crystal 2 and the second birefringent crystal 3 have the same thickness and their optical axes are perpendicular to each other, used to introduce a delay difference Δt between the first and second signal lights, where Δt = N × λ / 2, N = 1, 2, 3… The second aperture 9 and the third aperture 10 are both glass plates that block the central region and transmit the edge region, used to block the central region of the incident first and second signal lights and transmit the edge region, respectively.

[0043] The first signal light, after being transmitted through the first birefringent crystal 2, is reflected sequentially by the first reflecting mirror 4 and the concave mirror 6, and then focused onto the surface of the medium 7. After being reflected by the medium 7, it is transmitted through the edge region of the second aperture 9 to the first lens 11, and finally focused onto the balanced photodetector 13 by the first lens 11. Simultaneously, the second signal light, after being transmitted through the second birefringent crystal 3, is reflected sequentially by the first reflecting mirror 4 and the concave mirror 6, and then focused onto the surface of the medium 7. After being reflected by the medium 7, it is transmitted through the edge region of the third aperture 10 to the second lens 12, and finally focused onto the balanced photodetector 13 by the second lens 12. At this time, by moving the delay line 14, the light intensity of the first signal light and the light intensity of the second signal light under different delays can be sampled by the balanced photodetector 13, obtaining the fundamental frequency modulation intensity curves of the first and second signal lights under different delays, and thus obtaining the fundamental frequency modulation intensity difference between the first and second signal lights. In other embodiments of the present invention, the balanced photodetector 13 can also be replaced by a CCD, or by two spectrometers. Since the two spectrometers can only sample the light intensity of the first signal light or the second signal light respectively, and obtain the fundamental frequency modulation intensity curve of the first signal light and the fundamental frequency modulation intensity curve of the second signal light under different delays, they cannot directly obtain the fundamental frequency modulation intensity difference between the first signal light and the second signal light. Therefore, when using two spectrometers as a substitute, the operator needs to manually calculate the fundamental frequency modulation intensity difference between the first signal light and the second signal light.

[0044] To avoid affecting the first reflector 4 when moving the delay line 14, a certain gap needs to be maintained between the first reflector 4 and the second reflector 5. However, the gap between the first reflector 4 and the second reflector 5 cannot be too large, otherwise the signal light and pump light will not be able to pass through the first reflector 4 and the second reflector 5 respectively. Therefore, the present invention sets a gap of 1mm-2mm between the first reflector 4 and the second reflector 5, preferably 1mm. At the same time, in this embodiment, the first reflector 4 and the second reflector 5 are preferably D-shaped mirrors, with the two D-shaped mirrors symmetrically arranged on both sides of the gap, and the side closer to the gap being a straight edge. This design reduces the footprint of the first reflector 4 and the second reflector 5 while forming a larger light spot.

[0045] Based on the aforementioned laser delay measurement device based on fundamental frequency optical modulation sampling, the present invention also provides a laser delay measurement method based on fundamental frequency optical modulation sampling, specifically including the following steps:

[0046] 1) Moving the delay line 14 changes the relative delay between the first signal light, the second signal light, and the pump light. The pump light, under different delays, perturbs the light fields of the first and second signal lights on the dielectric surface, forming a fundamental frequency modulation. The intensity of the first and second signal lights under different delays is sampled by the balanced photodetector 13. Figure 2 As shown, the fundamental frequency modulation intensity curves of the first signal light and the second signal light under different delays are obtained, and the fundamental frequency modulation intensity difference between the first signal light and the second signal light is obtained.

[0047] 2) Determine whether the fundamental frequency modulation intensity difference between the first and second signal lights output by the balanced photodetector 13 is 0. If it is, there is no delay between the two ultrashort pulse laser beams under test; if not, there is a delay between the two ultrashort pulse laser beams under test. Based on the fundamental frequency modulation intensity difference between the first and second signal lights, obtain the delay error between the two ultrashort pulse laser beams under test. Specifically, perform linear fitting on the fundamental frequency modulation intensity difference curve of the first and second signal lights, such as... Figure 3 As shown, the middle part of the two dashed lines is the fitting curve, and the linear coefficient between the laser delay and the fundamental frequency light modulation intensity difference is 2.21 / fs. For example, when the fundamental frequency light modulation intensity difference is 0.7, the delay error between the two ultrashort pulse lasers under test can be calculated as 0.7 / 2.21 = 0.3fs.

[0048] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A laser delay measurement device based on fundamental frequency optical modulation sampling, characterized in that: It includes a first aperture (1), a first birefringent crystal (2), a second birefringent crystal (3), a first reflector (4), a second reflector (5), a concave mirror (6), a medium (7), an obstruction (8), a second aperture (9), a third aperture (10), a first lens (11), a second lens (12), and a balanced photodetector (13); The first aperture (1) is located on the incident light path of the two ultrashort pulse lasers to be tested. The first aperture (1) has a large aperture and two small apertures of the same size. One incident laser beam passes through the large aperture and is used as pump light. The other incident laser beam is split into two beams through the two small apertures and used as the first signal light and the second signal light. The area of ​​the large aperture needs to ensure that the energy of the transmitted pump light is greater than 7 μJ. The area ratio of the small aperture to the large aperture is 1:25 to 1:

36. The first reflector (4) or the second reflector (5) is provided with a delay line (14) to change the relative delay between the first signal light, the second signal light and the pump light; The first reflector (4) and the second reflector (5) are located on the same plane when their relative delay is 0; The focal length of the concave mirror (6) is chosen to ensure that the pump light focusing intensity is greater than 5 × 10⁻⁶. 12 W / cm 2 ; The second reflector (5), the concave mirror (6), the medium (7), and the block (8) are located sequentially on the incident light path of the pump light; after the pump light is reflected sequentially by the second reflector (5), the concave mirror (6), and the medium (7), it is completely blocked by the block (8); The first birefringent crystal (2) and the second birefringent crystal (3) have the same thickness and their optical axes are perpendicular to each other, which is used to introduce a delay difference between the first signal light and the second signal light; the second aperture (9) and the third aperture (10) are both provided with a shield in the central region and the edge region is used for transmission. The first birefringent crystal (2), the first reflector (4), the concave mirror (6), the medium (7), the second aperture (9), the first lens (11), and the balanced photodetector (13) are located sequentially on the incident light path of the first signal light; after being transmitted through the first birefringent crystal (2), the first signal light is reflected sequentially through the first reflector (4), the concave mirror (6), and the medium (7), and then focused onto the balanced photodetector (13) through the edge region of the second aperture (9) and the first lens (11); The second birefringent crystal (3), the first reflector (4), the concave mirror (6), the medium (7), the third aperture (10), the second lens (12), and the balanced photodetector (13) are located sequentially on the incident light path of the second signal light. After being transmitted through the second birefringent crystal (3), the second signal light is reflected sequentially through the first reflector (4), the concave mirror (6), and the medium (7), and then focused onto the balanced photodetector (13) through the edge region of the third aperture (10) and the second lens (12).

2. The laser delay measurement device based on fundamental frequency optical modulation sampling according to claim 1, characterized in that: A gap of 1mm-2mm is maintained between the first reflector (4) and the second reflector (5); The distance between the two small holes and the large hole is greater than or equal to 2mm.

3. The laser delay measurement device based on fundamental frequency optical modulation sampling according to claim 2, characterized in that: The straight-line distance between two small holes on opposite sides is equal to the diameter of the large hole.

4. The laser delay measurement device based on fundamental frequency optical modulation sampling according to claim 3, characterized in that: The first reflector (4) and the second reflector (5) are D-shaped mirrors. The two D-shaped mirrors are symmetrically arranged on both sides of the gap, and the side closer to the gap is a straight edge.

5. The laser delay measurement device based on fundamental frequency optical modulation sampling according to claim 4, characterized in that: The gap between the first reflector (4) and the second reflector (5) is 1 mm; The distance between the two small holes and the large hole is 2mm; The spacing between the pinholes is 3mm.

6. The laser delay measurement device based on fundamental frequency optical modulation sampling according to claim 5, characterized in that: The medium (7) is fused silica or SiO2.

7. The laser delay measurement device based on fundamental frequency optical modulation sampling according to claim 6, characterized in that: The second aperture (9) and the third aperture (10) are both thin glass sheets with central area blocking and edge area transmission.

8. A laser delay measurement device based on fundamental frequency optical modulation sampling according to any one of claims 1-7, characterized in that: The delay line (14) is formed by placing the first reflector (4) on a movable platform and moving the movable platform back and forth in a direction perpendicular to the first reflector (4); The mobile platform is a piezoelectric ceramic displacement stage.

9. A laser delay measurement device based on fundamental frequency optical modulation sampling according to any one of claims 1-7, characterized in that: The delay line (14) is formed by placing the second reflector (5) on a movable platform and moving the movable platform back and forth in a direction perpendicular to the second reflector (5); The mobile platform is a piezoelectric ceramic displacement stage.

10. A laser delay measurement method based on fundamental frequency optical modulation sampling, based on the laser delay measurement device based on fundamental frequency optical modulation sampling as described in any one of claims 1-9, characterized in that, Includes the following steps: 1】Moving delay line (14) uses pump light at different delays to perturb the light fields of the first signal light and the second signal light on the surface of the medium to form fundamental frequency light modulation. The light intensity of the first signal light and the light intensity of the second signal light at different delays are sampled by a balanced photodetector (13) to obtain the fundamental frequency light modulation intensity curve of the first signal light and the fundamental frequency light modulation intensity curve of the second signal light at different delays, and then outputs the fundamental frequency light modulation intensity difference between the first signal light and the second signal light. 2】Determine whether the fundamental frequency modulation intensity difference between the first signal light and the second signal light output by the balanced photoelectric probe (13) is 0. If it is, there is no delay between the two ultra-short pulse lasers to be tested. If not, there is a delay between the two ultra-short pulse lasers to be tested. The delay error between the two ultra-short pulse lasers to be tested is obtained based on the fundamental frequency modulation intensity difference between the first signal light and the second signal light.

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